Line drop compensator



Jan. 7, 1941. T F. M. STARR I Re. 21,687

V LINE EH61 COMPENSATOR I l 7 Original Filed Nov. 24, 1937 H s Attorney.

Reissued Jan. 7, 1941 PATENT OFFICE LINE DROP COIVIPENSATOR rein: M. Starr, Schenectady, N. Y., a ssignor to General Electric Company, a corporation of New York Original No. 2.1135315, dated January 2, 1940, Sem1 No. 176,293, November 24, 1937. Application for reissue November 6, 1940, Serial No.

. 16 Claims.

This invention relates .to line drop compensa tors and it has for an object the production of an improved lin'e drop compensator in which a true reactance setting may easily be secured. Another object of the invention is to produce a line drop compensator in which a true reactance setting and a true resistance setting are made by adjusting separate slide wire resistors.

A line drop compensator is a device which compensates a voltmeter for the voltage drop in a line between the point on the line to which the meter is connected and any other point on the line at which it is desired 'to knowthe voltage. In alternating current circuits, the voltage drop in a line always contains both a resistance component and a reactance component and consequently line drop compensators for such circuits are usually provided with an adjustable resistance element and an adjustable reactance element. The resistance element has usually been the equivalent of an ordinary rheostat. in which adjustment is made by sliding an arm over a resistance wire. The reactance element, how. ever, has usually been a reactor or reactance 8| transformer provided withtaps for securing adjustment. Because of its greater cost, and the necessarily limited number of-taps, this way of securing adjustable reactance compensation has not been as good as the simple slide wire resistor adjustment of the resistance element.

In accordance with this invention, there is provided a novel and simple compensator in which .true reactance compensation may easily and inexpensively be secured and in. which this compensation may be adjusted in exactly the same manner as the resistance compensation, namely, by means of a slide wire resistor. By true reactance compensation is meant .the production by the reactance element of a voltage in the voltmeter circuit which is a true reflection in magni tude and phase of the reactance voltage drop in the main line.

The invention will be better, understood from .the following description taken in connection line 2. The regulator I may be of any well known type such, for example, as an induction regulator or a step regulator. This regulator is driven by a conventional reversible motor 3 whose direction of operation is controlled by the raise and lower contacts'of a primary relay or contact making voltmeter 4. Both the motor andthe contact making voltmeter are energized from the, secondary winding of a potential transform- I the power line 2.

The line drop compensator consists of aretsistance element in the form of slide wire resistor 8 and a reactance element in the form of a second slide wireresistor I combined with a capacitor 8 and a reactor 9 connected in series across the resistor The compensator is energized in accordance with the current in the power line 2 by means of a current transformer Ill.

The capacitor 8 and reactor 9 are so proportioned that their respective reactances are equal to each other at the rated frequency of the power line. As this amounts toa condition of series resonance, it may sometimes be desirable to limit the current in these elementsby means of a relatively small auxiliary series resistor 'II. The invention, however, in no wise depends on the presence of this auxiliary resistor.

The connections between the compensator and the primary relay are such that the resistance element 6 and the reactance element 9 are con nected in series with the operating winding of the primary relay 4 across the secondary'winding of the potential transformer 5.

The operation of the compensator is as follows. The current transformer current will divide through the two parts of the resistor 1, some of the current flowing through the left hand portion of I and the remainder of the current er 5, whose primary winding is connected across flowing through the right hand portion of I and then through the reactance elements 8 and 9 (and the auxiliary resistor II) in series until it ioins the current through the. left hand part of the resistor I whereupon the two currents rejoin and return through the portion of the slide wire resistor 6 which is determined by the latters setting. As the reactance elements 8 and ii are numerically equal to each other and of opposite sign, they have practically no effect on the division of current and this current will therefore divide inversely as the resistances of the two parallel branches. Ifthe total resistance of I is R, and the resistance of the portion thereof to the right of the adjustable slide wire is r, and that of the auxiliary current limiting resistor is n, the transformer current will divide in- 'thereactancecompensationwillbe ILLI?) is Asthecurrenttransformer currentisactually onlylimitedbyresistancethecurrentthrough thereactorlwillbepracticallyinphasewiththe line current and consequently the voltage drop throughthereactortwillbedisplacedWJn 20phasefromthelinecurrent.

-Aswillbeseenfromthe agedrop across the reactor I is directly gmseries with the operatin'g coil of the primary Alsoin serieswith the operating coil of the primaryrelaylistheresistortofthcresistance element of the compensator and consequently. depending upon the setting of-the' slide wireon' this resistor-yen adjustable voltage is in 30 phase opposition tothe current in the line I. and

consequentlywhichisinphasewiththeresist-.

ancevoltagedropinthe line.isinsertedin' the primary relay or voltmeter circuit.

Thesevector relations can be seen more clear-- a5 ly from Fig. 2 in which the long horisontal vector labeled Va is the voltage of the secondary windingof the potential transformer and the vector labeled I represents a lagging current in the line I. VectorIRisthe voltagedropinserted inthe' 4 contact making voltmeter circuit by the resistance element 8 of the'linedrop compensator and vbysimplyaniiustingthepositionoi the slidewire on this element; the vector IR ,may be made to bear exactly the same relation to thesecondary 45 voltage ofthe potential transformer Vpasexists betweentheactualresistancedropinthelinel andthelinevoltage. Theequslandopmslte Vectors 1x1 and Ixs. which are'both at i tf' angles to the vector IR,represent the individual voltagedropsacrossthe'reactor I andthecapacitor I respectively. By simply adjusting the position oftheslidewireon the Lashas been previously explained, the magnitude of the voltage drop 1X1. which is'inserted in the contact makingvoltmetercirclut, ca'nbeadiusted atwill I and can readily-be made to bear the samerelation to the potential transformer voltage V3 as existsbetweentheactualreactimcedropinthr line I and the line voltage. The .vector Vm represents the voltage applied to the operating wi ndingoi'the'contactmahingvoltmeterandis the vector sum of thepotentlal transformer.

f voltagea'ndtberesistance'andreactanceelement voltages of the line drop compensator.

In the automatic voltagereguiating M: shown in. Hg. 1. the operation isalways such so tomaintainconstantvoltsgeacrossthewlnding ofthecontactmakingvoltmeter. 'Ihisisbecameifthevoltageappliedtothevoltmeterfslls goi il tly below a normal valueQits raise contacts .will energise the motor ior such direction of operation as to cause the regulatortoraisethevoltageof lun'tilthe raisewntactsadlinmtegh 1| operationtakesplacaincalsethe inductive reaotance ms value x;. it

voltageoiline I rises a small amount above normal. to cause the contact making voltmeterto close its lower contacts. That is to say the motor will-be reversed the regulator will lower the voltage until the lower contactaagain separate.

It will thus be seen that the vector Vs stays constant in magnitude and that changes in the [magnitude orphase angle or bothof the current vector I will change the values of the resistance and reactance drops IR and lxrwith the result that the voltage of. the potential trantformer secondary will be changed, by means of the regulator. until a new value oi V is reached at which the vector sum of the constant contact making voltmeter voltage and the variable resistance and reactance drops will equal the potential transformer voltage. p v 7 It should be noted that the capacitor 8 is an important feature of the invention and makes it possible easily to secure true reactance compensation. Thus. if the capakzitor was omitted, the voltage dropacross the reactor I would only be in quadrature with the current transformer current when the impedance of the reactor was inilnitelyless than the resistance It ofresistor I. I'ibr practical ratios of these values an appreciable error would be introduced in the reactance compensation. The series resonance produced by capacitor I reduces'the impedance of the branch containing the reactor to a value which is almost infinitely less than a practical value of resist- V ance R of resistor f andthus produces practically true and errorless reactance compensation. In the above description the simplifying assumption has tacitly been made that the reactor 0 is a pure reactor containing no inherent resistance. I While this is only possiblein theory it is possible'by special construction, resulting in; a relatively large and expensive reactor, to produce a reactance device having anegligible amount of resistance in comparison with its reactance. Most commercial reactors and those which are made up to have a'relatively large reactance for their size inherently have an appreciable amount of resistance. When such a reactor is used true as reactance compensation will be obtained with my invention because the series capacitor 8 will be so proportioned with respect to the constants of the reactor; that the voltage drop across the reactor will be in phase with the reactance voltage drop in the main circuit 2. I

While there is shown and described a particular embodiment of this invention it will be obvious tothose skilledintheartthat cha'ngesandmodifications can be made without departing from this invention. and it is therefore aimed. in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention. 1,

What I claim as new and desire to secure by Letters Patent of the United States, is: 1. In a line drop compensated voltage sensitive system. an alternating current line. a voltage measuring device connected to respond to the voltageat a point onsaidline. ailxed reactor 65 connected in circuit with said voltage measuring device. means forhcausing an alternating current which is pr p rtional to the current in said line to iiow'through said reactor, means for ad- I lusting the ratioof the line current to, the re-"IO actor current and means for causing the reactor current to be'suhstantially in phase with; the line current at any adjusted ratio of said currents. ,2. In a line drop compensated voltage sensitive system. an alternating current line. a voltage is 21,687 measuring device connected to respond to the to flow through said reactor, a slide wire resistor.

for adjusting the ratio of the line current to, the reactor current, and a capacitor for causing the reactor current to be substantially in phase with the line current at any adjusted ratio of said currents.

3. In a line drop compensator, an adjustable reactance element comprising two electrically parallel branches, one of said branches containing serially connected numerically equal inductive and capacitive reactance devices, variable resistors in each of said branches, and means for simultaneously and oppositely adjusting the values of saidresistors.

4; In a line drop compensator, an adjustable reactance element comprising series resonant reactance, devices, means for circulating therein a current proportional to the current" in an alternating current line, afid a slide wire resistor for adjusting the ratio of the current in said devices to the current in said'line.

5. In a compensated voltage sensitive system, a line drop compensator comprising a pair of serially connected rheostats, a reactor and a capacitor connected in series with each other and in shunt with one of said rheostats, and a voltage sensitive circuit connected to contain the other of said resistors and said reactor serially connected therein.

6. In a line drop compensated voltage sensitive system, an alternating current power line, a voltage measuring device connected to respond to the voltage at a point on said line, a fixed reactor connected in circuit with said device, a resistor and a capacitor in series with reactor, said reactor and capacitor having equal ohmic values at the normal frequency 01' saidv power line, a slide relay, a second 're'sistor'and a capacitor connectedwire adjuster on said resistor, and means for circulating a current proportional to the current in said line between said slide wire adjuster and a point of the circuit on said measuring device outside said resistor.

'7. In combination, an alternating current power line having a normal frequency, an automatic voltage regulator therefor, a primary relay for controlling said regulator, said relay being connected to respond to the voltage of said line, and a line drop compensator for said relay and regulator comprising a resistor and a reactor connected in seriesin circuit with said primary in series with each other and in parallel with said reactor, said reactor and capacitor having equal ohmic values at the normal frequency of said line, separate slide wire adjusters on each of said resistors, and a currenttransformer having its primary winding in said line and the terminals of its secondary winding connected respectively to said slide wire adjusters.

8. In a line drop compensator for adapting an automatic voltage regulator to maintain constant voltage at a distant point on an alternating current power circuit, a reactive device, means for circulating through said device a current derived from the power current in said circuit, and

9. In a line drop compensator for adapting an automatic voltage regulator to maintain constant voltage at a'distant point on an alternating current power circuit, a reactive device, means for circulating through said device a current derived from the power current in said circuit, means for adjusting the ratio of said circuit current to said reactance device current, and means for causing the phase relation of said currents to be such that the voltage drop across said device is' in phase with the reactance voltage drop in said power circuit.

10. In a line drop compensator for adapting- ,an automatic voltage regulator to maintain con voltage drop in said power circuit.

stant voltage at a distant point on an alternating current power circuit, a reactive device, means for circulating through said device a current derived from the power current in said circuit,

and opposite sign reactive means connected in series with said reactive device with respect to said circulating current for causing the phase relation of said currents to be such that the voltage drop across said device is in phase with the reactance voltage drop in said power circuit.

13. In a line drop compensator for adapting an automatic voltage regulator to maintain constant voltage at a distant point on an ,alternat-. ing current power circuit, an inductive react-' ance device, means for circulating through said device a current derived from the power current in said circuit, means comprising a slide wire adjustable type impedance element connected in parallel with said reactance device for adjusting the ratio of said circuit current to said reactance device current, and a capacitor connected in series with said reactance device with respect to said circulating current for causing the phase relation of said currents tobe such that the voltage drop across said device is in phase with the reactance voltage drop in said power circuit.

14. In a line drop compensated voltage sensitive system, an alternating current line, a voltage measuring device connected to respond to the voltagelat a point on said line, a reactive device, means for circulating through said reactive device 'a current derived from the power current in said line, adjustable impedance means in parallel circuit relation with said reactive device for varying the ratio of said currents, and

means tor causing the phase relation of said currents to, be such that the voltage drop across said reactive device'is in phase with the reactance voltage drop in said power line.

ii. In a linedrop compensated voltazesensitive'systemanal'ternatingcurrentlinmavoltagemeasuringdeviceconnectedtorespondtothe voltage at-a point on said line. a reactive device. means for circulating through said reactive de- -vice a current derlved'irom thepower current in said line. meinsincluding a rheostat connected in parallel circuit relation with said reactive device for adjusting the. ratio oi said line current to said reactive device current. and

. means for causing the phase relation of said curre'utstohesuchthatthevolmedmacross said reactive devicels in phase withthe reactancevoltagedropin' power circuit at-anycurrents.

adiustcdratio of said sneer 1 mm combination, an alternating. current power line, an automatic voltage regulator there for-{a primary relay for controlling said regu-,

later. said relay being connected to respond to' the voltage of said line, and a line drop compensator for said relay and said-regulatoracomprising a resistor and a reactor connected in series in circuit with said primary relay, a second resistor and a capacitor connected in series with each other and in parallel with. said reactor,

and a current transformer having its primary 

